1. Field
Aspects of embodiments of the present invention relate to a secondary battery.
2. Description of the Related Art
Lithium ion secondary batteries are widely used in small electronic devices, such as notebook computers and cellular phones. Such lithium ion secondary batteries are superior to other types of secondary batteries in terms of power, capacity, and weight, and can also be used in hybrid vehicles and electric vehicles.
Lithium ion secondary batteries for vehicles should satisfy the requirements of safety and reliability under harsh conditions. A penetrating test, a squeezing test, and an overcharging test are the harshest ones of safety tests.
Of these safety tests, the penetrating test is very important in predicting damage to a secondary battery due to a vehicle accident. Particularly, the penetrating test requires that even after a nail penetrates a secondary battery, the temperature of the secondary battery does not excessively increase, or the secondary battery is not ignited or burned.